1. Field of the Invention
The present invention relates generally to hard copy apparatus and, more specifically, to a method and apparatus for deskew of a fed sheet using spherical drive mechanisms with independent axial drives.
2. Description of Related Art
It is well known that a cut sheet piece of print media must be appropriately aligned to the associated printing mechanism if a true print of the data or a true copy of a document is to be successfully rendered. Problems associated with the variety of prior art mechanisms--such as spring-loaded side guides and canted rollers used to drive d sheet into and along a side wall--are exacerbated by the fact that it is difficult to tune a hard copy paper transport subsystem to work identically with a broad range of print media weights and sizes available to the end user. Spring-loaded side guides are sensitive to the parallelism of the side edges and the width of the sheet. Side guides do not give predictable alignment or edge position due to the inaccuracy of the paper cutting process. The edges of the sheet will generally not be perfectly parallel. As the side guides are attempting to align on both edges simultaneously, it is unpredictable which edges will end up dominating the alignment. For this same reason, the location of the edge of the sheet is unpredictable. The stiffness of the media being aligned will also vary and in some cases the force imparted by the side guides will cause the edge of the sheet to buckle. In addition to possibly damaging the sheet, this further reduces the predictability of the sheet position and orientation.
Canted rollers may slip on the sheet surface and cause damage to soft-coated media. Media type settings that work well for relatively lightweight media--e.q., plain paper-are often ineffective for relatively heavyweight media--e.g., card stock, letter size envelopes, and overhead transparencies. Settings that work for stiffer media frequently damage relatively flexible media.
There is a need for a deskewing system that works effectively over a broad range of media weights, sizes, and types.
[For convenience of description, print media of all shapes, sizes, and varieties are referred to hereinafter simply as "media," "sheet," or "paper" as best fits the context; no limitation on the scope of the invention is intended by the inventors, nor should any such limitation be implied.]